Soda-lime-silica glass is an amorphous inorganic material comprised of a network of spatially cross-linked silicon dioxide (SiO2), sodium oxide (Na2O), and calcium oxide (CaO), plus other optional oxide and non-oxide materials. The silica component is the largest oxide by weight and constitutes the primary network forming material of the glass. The sodium oxide and calcium oxide components are glass network modifiers that serve, respectively, as a fluxing agent and a stabilizer. In particular, the sodium oxide component reduces the viscosity of the glass at a given temperature and makes the glass more workable, and the calcium oxide component reduces the viscosity of the glass at high temperatures while also adding chemical resistance (most notably to water) to the glass. Soda-lime-silica glass has a chemical composition that includes 60 wt % to 80 wt % silica, 8 wt % to 18 wt % sodium oxide, 5 wt % to 15 wt % calcium oxide, and optionally 0-2 wt % aluminum oxide (Al2O3), 0-4 wt % magnesium oxide (MgO), 0-1.5 wt % potassium oxide (K2O), 0-1 wt % iron oxide (Fe2O3), 0-0.5 wt % titanium oxide (TiO2), and 0-0.5 wt % sulfur trioxide (SO3), among others. Owing to its good chemical stability, workability, and cost, soda-lime-silica glass is an attractive option for three-dimensionally-shaped glass articles including containers such as bottles and jars.
Glass articles composed of soda-lime-silica glass have long been made by a melt processing route that involves melting a pre-formulated batch of reactant materials at high temperatures into workable molten glass with the proper chemistry as well as the proper chemical and thermal consistency before conducting additional downstream glass forming operations. The batch reactant materials have conventionally included a physical mixture of virgin raw materials and, optionally, recycled glass materials known in the industry as “cullet.” The virgin raw materials contain quartz sand (crystalline SiO2), soda ash (Na2CO3), and limestone (CaCO3) in the appropriate proportionate amounts needed to attain the requisite molar ratio of SiO2, Na2O, and CaO, respectively, in the final glass composition. Additionally, to further tailor the characteristics of the resultant glass and/or to enhance glass workability, the virgin raw materials may include small amounts of other ingredients including feldspar, which is a source of Al2O3, precursors to other glass network formers and glass network modifiers, colorants, decolorants, fining agents, and redox agents. Cullet from consumer and/or commercial products may be combined with the virgin raw materials and, if used, has typically constituted up to 80 wt % of the batch reactant materials.
In most high-volume, melt process glass manufacturing operations, the batch reactant materials are melted by a continuous process in a refractory brick-lined furnace at temperatures above 1200° C. To begin, the batch reactant materials are introduced, or “charged,” at a controlled rate into a primary melting section of the furnace using any method of batch charging such as a screw conveyor, mechanical pushing mechanism or other. Specifically, the batch reactant materials are deposited as a batch blanket on top of a flowing molten glass bath, which is heated and maintained in a molten state by the combustion of fuel oil or natural gas in the space above the bath through the operation of burners (e.g., a regenerative side-port burner configuration). Over time, the various batch reactant materials are melted through dissolution, decomposition, and/or melting reactions at temperatures that can exceed 1500° C. The various batch reactant materials progress through several intermediate melt phases and eventually become chemically integrated into the flowing molten glass bath as the bath moves by convection through the primary melting section of the furnace towards a refining section on the opposite side of a submerged throat. In the refining section of the furnace, the molten glass bath is refined at a temperature between 1400° C. and 1550° C. to remove entrained gas bubbles with or without the help of chemical refining agents. Gas bubbles are primarily introduced into the molten glass bath when, among other mechanisms, carbonate-containing batch materials such as Na2CO3 and CaCO3 decompose during melting of the batch reactant materials to evolve carbon dioxide.
The refining section of the furnace yields chemically homogenized and refined molten glass having the correct chemistry as needed for further processing into a glass article. To that end, when manufacturing hollow glass articles such as glass containers, molten glass is removed from the furnace at the refining section and transported through a forehearth to a glass feeder. The forehearth is an extended channel that functions to cool the molten glass at a controlled rate to a working temperature and viscosity suitable for glass forming operations while also achieving a more uniform temperature profile within the molten glass. At the glass feeder, the conditioned molten glass is formed into streams that are sheared into molten glass gobs of a predetermined weight. The molten glass gobs are then delivered by gob delivery systems into individual section machines where they are fashioned first into partially-formed containers known as parisons and then into finished glass containers by the blow-and-blow method or the press-and-blow method. Upon emerging from the individual section machine, the finished glass container is cooled to preserve its shape and then annealed in one or more annealing lehrs, typically at a temperature between 550° C. and 600° C., to remove internal residual stress points within the container. Any of a variety of external coatings may be applied to the exterior container surface before and/or after annealing, if desired.
The manufacture of glass containers by the melt processing route is thus a demanding process in terms of time and energy consumption. The melting and refining processes that occur in the furnace require the greatest investment of time and energy as each unit of batch reactant materials that corresponds to a finished glass container has a residence time in the furnace that typically exceeds 24 hours. Such a long residence time is primarily due to the initially slow dissolution rate of crystalline quartz sand, the time needed to homogeneously chemically mix the melted batch reactant materials into the molten glass bath—especially the quartz sand which has a tendency to agglomerate into SiO2-rich regions known as “cord”—and the time needed to refine the molten glass to effectively remove entrained gas bubbles before further downstream processing can occur. And, while the substitution of cullet for virgin raw materials in the batch reactant materials can accelerate the melting of the reactant materials and lower furnace energy consumption, mainly because the cullet has already been formed into a glass product and will not release carbon dioxide when melted, current melt processing practices still typically require furnace residence times of at least 24 hours. This is because cullet has a tendency to be contaminated with metals, glues, and other organic compounds, and is sometimes difficult to uniformly mix with virgin raw materials into the flowing molten glass bath, and also because bulk purchases of cullet are subject to great variations in color and other characteristics.
The present disclosure describes a way to manufacture a hollow glass article composed of soda-lime-silica glass and having a container shape. The method involves forming the hollow glass article from a particulate feedstock comprised predominantly of soda-lime-silica cullet particles while avoiding the conventional melt processing route. The disclosed method, in particular, forms the hollow glass article composed of soda-lime-silica glass without melting the cullet particles in the particulate feedstock, but, rather, by mechanical working and solid-state sintering operations that are carried out at temperatures that do not exceed 850° C. Because the cullet particles are fused in the solid-state during sintering, as opposed to being melted and refined in a furnace, the disclosed method consumes significantly less energy from start to finish, thus reducing the carbon footprint of each manufactured hollow glass article compared to conventional melt processing. The disclosed method additionally lowers capital equipment and maintenance costs, simplifies raw material handling, and dispenses with the need to handle molten materials during formation of the hollow glass article. These attained benefits can drastically change the glass container manufacturing infrastructure.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other to make a hollow glass article having a container shape and composed of soda-lime-silica glass. The glass composition associated with the soda-lime-silica glass article comprises 60 wt % to 80 wt % SiO2, 8 wt % to 18 wt % Na2O, and 5 wt % to 15 wt % CaO, plus other optional oxide components such as, for example, aluminum oxide, magnesium oxide, and/or potassium oxide, depending on the composition of the soda-lime-silica cullet used to prepare the particulate feedstock. The glass transition temperature of the soda-lime-silica glass lies within the range of 510° C. to 600° C. The hollow glass container-shaped article formed by practices of the disclosed method can take on a variety of three-dimensional container-shaped configurations including, for example, a partially-formed container (i.e., a parison) or a finished container in the form of a bottle or jar.
According to one aspect of the present disclosure, a method of making a hollow glass article composed of soda-lime-silica glass comprises pulverizing soda-lime-silica cullet to obtain cullet particles of a reduced particle size and incorporating those particles into a particulate feedstock. The particulate feedstock is then formed into a hollow monolithic glass container preform without melting the cullet particles contained in the feedstock. The hollow monolithic glass container preform has a temperature above the glass transition temperature of the soda-lime-silica glass, but not in excess of 850° C., and further has a container shape that includes a wall defining an interior containment space and an opening to the interior containment space. After being formed, the hollow monolithic glass container preform is cooled into a hollow, amorphous, soda-lime-silica glass article that retains the previously-established container shape.
According to another aspect of the present disclosure, a method of making a hollow glass article composed of soda-lime-silica glass comprises incorporating soda-lime-silica cullet particles, regardless of how they are obtained, into a particulate feedstock. The particulate feedstock is then pressed into a compressed solid green-body. Thereafter, the compressed solid green-body is sintered at a sintering temperature above the glass transition temperature of the soda-lime-silica glass, but not in excess of 850° C., to fuse the compressed solid green-body into a solid monolithic glass body without causing recrystallization within the glass body. The solid monolithic glass body is then mechanically deformed into a hollow monolithic glass container preform having a container shape that includes a wall defining an interior containment space and an opening to the interior containment space. After being formed, the hollow monolithic glass container preform is cooled into a hollow, amorphous soda-lime-silica glass article that retains the previously-established container shape.
According to still another aspect of the present disclosure, a method of making a hollow glass article composed of soda-lime-silica glass comprises incorporating soda-lime-silica cullet particles, regardless of how they are obtained, into a particulate feedstock. The particulate feedstock is then pressed into a compressed hollow green-body that generally corresponds in size and shape to the hollow monolithic glass container preform sought to be formed. Thereafter, the compressed hollow green-body is sintered at a sintering temperature above the glass transition temperature of soda-lime-silica glass, but not in excess of 850° C., to fuse the compressed hollow green-body into a hollow monolithic glass container preform without causing recrystallization within the preform. The resultant hollow monolithic glass container preform has a container shape that includes a wall defining an interior containment space and an opening to the interior containment space. After being formed, the hollow monolithic glass container preform is cooled into a hollow, amorphous soda-lime-silica glass article that retains the previously-established container shape.